1. Field of the Invention
This invention relates to novel acetal copolymers. More particularly, this invention relates to novel low Tg (glass transition temperature) copolymers of trioxane and 1,3-dioxolane which, by virtue of having higher dioxalane contents than hitherto contemplated in the prior art, are non-crystalline at room temperature (about 25.degree. C.) or above, although they can be made to crystallize at temperatures below room temperature. These copolymers can be blended with conventionally prepared crystalline oxymethylene homo-, co- and terpolymers to improve the impact properties of molded articles made therefrom, and can also be used as adhesives for crystalline oxymethylene polymers as disclosed in commonly-assigned copending U.S. patent application Ser. No. 096,189, filed of even data herewith in the names of George L. Collins and Kurt E. Wissbrun.
2. Description of the Prior Art
Acetal or oxymethylene copolymers, including ones made from trioxane and dioxolane as the comonomer pair, are well known in the art. Such copolymers are characterized as having recurring oxymethylene groups or units, i.e., --CH.sub.2 O-- groups, interspersed with oxy(higher)alkylene groups or units, e.g., --CH.sub.2 CH.sub.2 O-- groups. They may be prepared, for example, as described in Walling et al U.S. Pat. No. 3,027,352 by copolymerizing trioxane, the source of the --CH.sub.2 O-- group, with a cyclic ether or cyclic formal having at least two adjacent carbon atoms, e.g., ethylene oxide, 1,3-dioxolane, 1,4-butanediol formal, and the like, in the presence of a catalyst, e.g., boron trifluoride diethyl etherate or the like.
Japanese Kokai Sho No. 42-22065, Yamada et al., published Oct. 30, 1967 discloses that the product of its Example 1, a trioxane/1,3-dioxolane copolymer, contained 64 mol % dioxolane, but says no more about this product.
Copolymers of 1,3-dioxolane and formaldehyde (which can be derived from trioxane) containing no less than 50 mol percent of oxymethylene units are disclosed in U.S. Pat. No. 3,639,347, issued Feb. 1, 1972 to Sugiura et al. These copolymers are disclosed as being in all cases tough, crystalline materials having melting points above 150.degree. C.
U.S. Pat. Nos. 3,598,788 and 3,639,192, issued Aug. 10, 1971 and Feb. 1, 1972, respectively, to Burg, disclose trioxane copolymers containing major amounts (in each case up to 60 weight percent) of comonomers such as dioxolane or 1,4-butanediol formal. The U.S. Pat. No. 3,598,788, however, describes its polymers as ones which can be used for "injection molding, extrusion, or deep drawing", and as grindable solids having melting points ranging from 70.degree. C. to 161.degree. C. The U.S. Pat. No. 3,639,192 specifically describes a material that is "tough and solid" and heat-meltable.
U.S. Pat. Nos. 3,379,655 and 3,422,035, issued Apr. 23, 1968 and Jan. 14, 1969, respectively, to May et al., broadly disclose trioxane/1,3-dioxolane copolymers wherein dioxolane "will make up between 0.01 and 50% of the units of the polymer" (see the U.S. Pat. No. 3,379,655 at column 1, lines 37-69 and the U.S. Pat. No. 3,422,035 at column 1, lines 35-69). Each of these patents also contains a working example in which 30 grams of dioxolane is copolymerized with 0.9 gram of trioxane (see Example 8 of the U.S. Pat. No. 3,779,655; Example 4 of the U.S. Pat. No. 3,422,035). However, the polymers obtained in these two working examples are characterized as having melting points of 54.degree.-55.degree. C. and 51.degree.-52.degree. C., respectively (the polymer of Example 4 of the U.S. Pat. No. 3,422,035 was processed by being "broken up and milled in acetone"), indicating that they were crystalline solids at room temperature.
In Example 4 of U.S. Pat. No. 3,337,507, issued Aug. 22, 1967 to Gutweiler et al, 1/3 mol of trioxane was polymerized with 1 mol of dioxolane, using p-nitrophenyldiazoniumfluoroborate catalyst, to give a clear, highly viscous oil at 70.degree. C. Upon cooling to room temperature, however, the polymer became a crystalline solid, since it was:
" . . . subsequently cooled in the polyethylene bag. The crystals were ground, boiled with methanol to which 1% of ethanol amine had been added and then dried." PA0 "The physical properties of the terpolymers can be varied within wide limits and depend, on the one hand, on the nature and concentration of the saturated cyclic formal or saturated cyclic ether and, on the other hand, on the concentration of the formal of an unsaturated cyclic diol. PA0 For example, when 0.1 to 10% by weight, calculated on the total monomer mixture, of unsaturated cyclic formal and 0.1 to 10% by weight, calculated on the total monomer mixture, of saturated cyclic formal or ether are used, highly crystalline products are obtained, whereas with 40 to 59.9% by weight, calculated on the total monomer mixture of unsaturated cyclic formal or ether, amorphous elastic glass-clear products are obtained. The more voluminous the second comonomer, the lower is the crystallinity and the higher is the elasticity. The decrease in crystallinity can be well measured by means of X-rays. PA0 Low molecular weight polymers which constitute waxes or oils can easily be obtained with the use of high concentrations of catalyst, that is about 0.1 to 1% by weight, calculated on the total monomer mixture. PA0 The above statements are intended to indicate the wide limits within which the properties of the terpolymers obtained by the process of the invention may be varied, the incorporation of different comonomers having, of course, different effects on the properties of the terpolymers and the transitions being fluid",
U.S. Pat. No. 3,194,788, issued July 13, 1965 to Kullmar et al, discloses in its Example 6 the polymerization of 5 parts by weight of trioxane with 15 parts of diethylene glycol formal, using p-nitrophenyldiazoniumfluoroborate catalyst, to give a colorless, thickly liquid oil which solidified to a wax-like mass on standing. No indication is given that non-crystalline behavior was obtained or is possible in this polymer.
Various dioxolane-containing acetal terpolymers are also known. For example, U.S. Pat. No. 3,848,020, issued Nov. 12, 1974 to Burg et al, discloses a trioxane/dioxolane/1,6-hexanediol formal terpolymer in which these three monomers were used in a 55:35:10 weight percent ratio. The terpolymer obtained had a melting point of 70.degree. C., indicating that it was a crystalline polymer.
U.S. Pat. No. 3,693,349, issued Feb. 1, 1972 to Burg, discloses trioxane/dioxolane/polyethylene oxide terpolymers which contain up to 60 weight percent dioxolane and may also contain a minor amount of a formal, glycidyl ether or prepolymer component. Polymers having "very good impact toughness coupled with good stability to alkalies" were obtained.
Trioxane/dioxolane/unsaturated diol formal terpolymers are disclosed in U.S. Pat. No. 3,297,647 to Schott et al. The patentees have this to say about their polymers:
column 2, lines 25-52. However, no high dioxolane content polymers are specifically disclosed, although Schott et al do state that "(t)he cyclic ether or saturated cyclic formal is advantageously used in an amount of 59.9 to 0.1% by weight, calculated on the total monomer mixture", and only terpolymers are disclosed.
None of the aforementioned patents or the published Japanese patent application teach trioxane/1,3-dioxolane copolymers which exhibit non-crystalline behavior at or above room temperature and low glass transition temperatures, or the use of such low Tg non-crystalline copolymers as impact property improvers for crystalline oxymethylene homo-, co- and terpolymers.